1. Field of the Invention
The present invention relates to an exposure method and exposure apparatus for transferring a pattern on a substrate while overlaying peripheral portions of pattern images of a mask, which is to be illuminated with exposure light, with each other.
2. Description of the Related Art
Conventionally, an exposure apparatus which projects a pattern image, formed on a photomask or reticle (hereinafter called xe2x80x9cmaskxe2x80x9d), onto a substrate on whose surface a photosensitive agent, such as a photoresist, is applied, via a projection optical system is generally used in manufacturing semiconductor devices, liquid crystal display devices, thin-film magnetic heads or the like through a photolithography process.
One way to cope with an enlargement of a substrate to be exposed is the use of a pattern synthesizing scheme which divides the exposure area of the substrate into a plurality of sub areas and repeats exposure according to the individual sub areas to finally synthesize patterns into a desired pattern. To prevent a seam of patterns at the peripheral portions of the individual exposure areas from being produced due to a writing error for a mask for pattern projection, the lens aberration of the projection optical system, a positioning error of a stage which positions a substrate, and so forth, exposure is carried out with the peripheral portions of the exposure areas overlaid with each other by a slight amount at the time of implementing the pattern synthesizing scheme. However, overlaying exposure areas leads to double exposure of the overlying portion, thus changing the line width at the overlying portion of pattern images. Further, the pattern synthesis produces a step (difference in height) at the overlying portion of patterns due to misregistration of adjoining exposure areas, which may degrade the characteristics of the devices. In the case where a step of overlaying multiple synthesized patterns one on another is assigned to a plurality of exposure apparatuses, an overlying error of exposure areas of the individual layers discontinuously at the seams of the patterns due to a variation in the lens aberration of the individual exposure apparatuses may occur. This significantly impairs the quality of devices.
Japanese Patent Application, First Publication No. Hei 6-244077, discloses a technique of eliminating the aforementioned problem of pattern synthesis. This technique uses a filter for reducing the amount of light transmission, provided at a position corresponding to the overlying portion of pattern images, so that the dose of the exposure light at the overlying portion of pattern images approximately matches the dose of the exposure light at other portions. Japanese Patent Application, First Publication No. Hei 6-302501, discloses a divisional exposure technique that uses a blind for continuously changing the illumination range of exposure light to a mask within the range that corresponds to the overlying portion of pattern images during exposure on a substrate. This technique likewise allows the dose of the exposure light at the overlying portion of the pattern images on the substrate to approximately match the dose of the exposure light at other portions.
Those methods are effective in that exposure can be carried out with the dose of the exposure light at the overlying portion of pattern images approximately matching the dose of the exposure light at other portions. Even if the light exposure quantities at the individual portions on a substrate coincide with one another, however, the shape of the pattern image to be formed on the substrate after development may vary at the individual positions of the overlying portion. If the first and second exposure positions at the overlying portion are slightly shifted, for example, the shape of the pattern image to be formed after development may vary at the individual positions due to a difference in resist sensitivity (the degree of a change in the shape of a pattern which is caused by a change in conditions, such as the developer used at the developing time and the developing time).
The dose of the exposure light at the overlying portion of pattern images on a substrate is adjusted based on the result of measurements by an illuminance sensor or the like. If this illuminance sensor has a measuring precision error, the actual dose of the exposure light at the individual positions of the overlying portion may vary.
In short, even with the dose of the exposure light adjusted by those methods, the line widths of actual patterns may vary from one position to another.
Accordingly, it is an object of the present invention to provide an exposure method and exposure apparatus which can form a pattern in such a way that the shape of the pattern matches an intended shape at each portion on a substrate at the time of transferring a pattern image of a mask illuminated with exposure light onto the substrate while overlaying peripheral portions of the pattern images with each other.
To achieve the above object, the present invention employs the following structures.
At the time of transferring a pattern image of a mask illuminated with exposure light onto a substrate, an exposure method according to the present invention performs exposure by overlaying peripheral portions of exposure areas with respect to a pattern image, which has previously been transferred onto the substrate, with each other, and adjusts the dose of the exposure light on the overlying portion based on a shape of a pattern image for an overlying portion formed on the substrate in such a way that the shape of the pattern image becomes an intended shape.
According to the present invention, the shape of a pattern image formed on the substrate is measured and the dose of the exposure light at the overlying portion is adjusted based on the measured result, so that the shape of the pattern image at the overlying portion can be matched with an intended shape without being affected by the measuring precision error of the illuminance sensor, a difference in resist sensitivity and so forth.
An exposure apparatus according to the present invention transfers a pattern on a substrate while overlaying peripheral portions of pattern images with each other, and comprises an illumination optical system which illuminates a mask with exposure light from a light source; a projection optical system which projects a pattern image of the mask onto the substrate; a dose adjusting device capable of adjusting a dose of the exposure light at the overlying portion; a shape measuring system which measures a shape of a pattern image of the overlying portion formed on the substrate; and a control system which controls the dose adjusting device based on a result of the measurement by the shape measuring system in such a way that the shape of the pattern image of the overlying portion formed on the substrate becomes the intended shape.
The dose of the exposure light at the overlying portion is adjusted by setting the dose of the exposure light at the peripheral portion of a pattern image in such a way as to become smaller in a direction away from a center of the pattern image and changing an overlying range of the peripheral portions of pattern images.
In this case, the exposure area is determined by a light-shielding section; and the dose of the exposure light at the peripheral portion can be set by continuously changing a moving speed of the light-shielding section which displaces in synchronism with exposure.
The above setting can be implemented by the dose adjusting device which comprises a light-shielding section capable of arbitrarily setting an area on the mask to be illuminated with the exposure light; and a light-shielding-section displacing device which displaces the light-shielding section in such a way that a dose of the exposure light at the peripheral portion of the pattern image becomes smaller in a direction away from a center of the pattern image in synchronism with exposure.
The light-shielding-section displacing device may be designed to be able to arbitrarily set a displacement start position of the light-shielding section, so that the range of the overlying portion can be set arbitrarily.
The light-shielding-section displacing device may be designed to be able to arbitrarily set a displacement speed of the light-shielding section, so that the distribution of exposure light in the range of the overlying portion can be adjusted.
Alternatively, the exposure area may be determined by a light-shielding section including a light-reducing member having a light-reducing characteristic which makes a light transmittance smaller in a direction away from a center of the pattern image; and the dose of the exposure light at the peripheral portion may be adjusted by changing an area of an overlying portion formed by the light-reducing member by using the light-reducing member.
The determination of the exposure area and the dose adjustment mentioned previously are carried out by the dose adjusting device. This dose adjusting device comprises a light-reducing member which is provided at a periphery of an opening and passes the exposure light so as to make a light transmittance smaller in a direction away from a center of the opening; and a light-reducing-member position adjusting device which adjusts a position of the light-reducing member.
The exposure apparatus may further comprise a dose measuring system which measures a dose of the exposure light at the overlying portion of a pattern image to be irradiated on the substrate and a dose of the exposure light at other portions than the overlying portion. This structure makes it possible to measure the dose of the exposure light on the substrate and uniformly adjust the dose of the exposure light on the substrate based on the measured result.
A device production method according to another aspect of the present invention comprises: exposing a predetermined pattern on a substrate using the above exposure method; and developing the substrate after the exposure.
In a device production method according to another aspect of the present invention, devices are produced by exposing a plurality of patterns on a substrate while overlaying peripheral portions of the patterns on each other to form an overlying portion. This device production method comprises: a step of adjusting an amount of overlaying of the peripheral portions so as to change light exposure quantities in the overlying portion and in non-overlying portions which are adjacent to the overlying portion; and a step of exposing the plurality of patterns on the substrate based on the adjusted amount of overlaying.
The step of adjusting may comprise: a step of measuring a pattern shape of the overlying portion exposed on the substrate; and a step of obtaining an amount of overlaying of the peripheral portions based on the pattern shape measured in the step of measuring.